1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of reporting link quality for radio blocks using various modulation schemes in an enhanced general packet radio service system (EGPRS) or an enhanced general packet radio service phase 2 (EGPRS2) system and to a method of requesting uplink radio resources from a mobile station to a base station.
2. Related Art
Global system for mobile communication (GSM) is a radio technology which has been developed as a standardized system for radio communication systems in Europe and which has widely been deployed all over the world. General packet radio service (GPRS) was introduced to provide packet switched data services in circuit switched data services provided by the GSM. The enhanced data rate for GSM evolution (EDGE) employs an 8-phase shift keying (PSK) in addition to the Gaussian minimum shift keying (GMSK) employed in the GSM. The enhanced general packet radio service (EGPRS) represents the GPRS using the EDGE.
A packet data channel (PDCH) denotes a physical channel used for GPRS/EGPRS traffic. Examples of logical channels mapped onto the PDCH include a packet common control channel (PCCCH) used for control signals required in packet transmission initialization, a packet data traffic channel (PDTCH) for user data, a packet associated control channel (PACCH) for dedicated signalling, and so on.
An enhanced general packet radio service phase 2 (EGPRS2) supporting further various modulation and coding schemes has recently being developed. While the EGPRS supports only two modulation schemes (i.e., GMSK and 8-PSK), the EGPRS2 supports five modulation schemes (i.e., GMSK, quadrature phase shift keying (QPSK), 8-PSK, 16-quadrature amplitude modulation (QAM), and 32-QAM). There are two levels of EGPRS2, that is, EGPRS2-A and EGPRS2-B. The EGPRS2-A supports the GMSK, 8-PSK, 16-QAM, and 32-QAM. The EGPRS2-B supports the GMSK, QPSK, 16-QAM, and 32-QAM. A downlink EGPRS2-A uses modulation schemes MCS-1 to MCS-4 (MCS stands for Modulation and Coding Scheme) and DAS-5 to DAS-12 (DAS stands for Downlink level A modulation and coding Scheme). An uplink EGPRS2-A uses modulation schemes MCS-1 to MCS-6 and UAS-7 to UAS-11 (UAS stands for Uplink level A modulation and coding Scheme). A downlink EGPRS2-B uses modulation schemes MCS-1 to MCS-4 and DBS-5 to DBS-12 (DBS stands for Downlink level B modulation and coding Scheme). An uplink EGPRS2-B uses modulation schemes MCS-1 to MCS-4 and UBS-5 to UBS-12 (UBS stands for Uplink level B modulation and coding Scheme). A modulation and coding scheme for each level in the EGPRS2 may be found in clause 6.5.5.1.3 of 3GPP TS 43.064 V7.6.0 (2007-08) “Technical Specification; GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS); Overall description of the GPRS radio interface; Stage 2 (Release 7)”.
An EGPRS/EGPRS2 system provides a multi-data rate by using various modulation and coding schemes. For example, data is transmitted with various data rates through the PDTCH. The data rate is regulated on the basis of the link quality in a link adaptation process. If the link quality is good, data is transmitted with a high data rate. On the contrary, if the link quality is poor, data is transmitted with a low data rate. Data may be lost when transmitted according to a modulation and coding scheme that requires a data rate higher than achievable with the link quality. In link adaptation, a data throughput is increased using the highest possible data rate by using a specific modulation and coding scheme with a predetermined link quality.
For the link adaptation process, the link quality needs to be reported from a mobile station (MS) to a base station (BS). In order for the MS to transmit packet data to a network, uplink radio resources have to be assigned. As described above, the EGPRS2 supports additional modulation schemes, and the MS supports the two EGPRS2 levels (i.e., EGPRS2-A and EGPRS2-B).
In the EGPRS/EGPRS2 system, the link quality between the base station and the mobile station is represented with a bit error probability (BEP). The BEP is an expectation value of the actual bit error rate (BER) of a signal received by the mobile station through a radio channel. The BEP is measured burst by burst. The base station selects a suitable modulation and coding scheme according to the reported link quality.
The link adaptation can be performed in a most effective manner when the reported BEP most accurately estimates the actual BER. With the use of additional modulation schemes in the EGPRS2, there is a need for a method of effectively reporting link quality according to the various modulation schemes.